Moisture-curable thermosetting polyurethanes are widely known as protective and decorative coatings or films in a broad range of applications, such as for example, coatings or films for walls, buildings, machinery, vehicles, equipment and other surfaces in need of a protective coating. These moisture-curable polyurethanes are prepared from polyisocyanate oligomers or prepolymers.
Moisture-curing polyurethane coating systems include a polyisocyanate oligomer component which reacts with atmospheric water at room temperature to form useful films. These systems also include pigments, organic solvents, and a variety of adjuvant components, e.g., surface active agents, dispersants, diluents, and fillers. This type of coating is one of the finest coatings available that can be produced without the application of heat or other external sources of energy. These systems are very useful for objects that cannot be heat-cured, such as buildings, large machinery, airplanes, ships and vehicles.
Two component thermosetting polyurethanes are widely used in protective coatings or films in a broad range of applications, such as for example, coatings for automotive machinery, equipment, and other surfaces in need of a protective coating. These room temperature-curable polyurethanes are prepared from polyisocyantes.
Two component polyurethane coating systems include a polyisocyanate component which reacts with polyol resin, such as an acrylic polyol or polyester polyol, to form useful films. The system also includes pigments, organic solvents, and a variety of adjuvant components, e.g., surface active agents, dispersants, diluents, and fillers. This type of coating is one of the finest coatings available that can be produced without the application of heat or other external sources of energy. They are very useful for objects that cannot be heat-cured, such as large machinery, airplanes, ships and vehicles.
Since the polyisocyanate component reacts with even trace amounts of moisture, extreme care must be taken so that the polyisocyanate does not contact water until they are applied to a surface to be coated. Water is, however, unintentionally and unavoidably introduced into the formulation process in the form of dissolved water in solvents, adsorbed and absorbed water in fillers and pigments, and atmospheric moisture. Subsequent reaction of the water with the polyisocyante component of the system results in an irreversible reaction which will produce carbamic acid. The carbamic acid is unstable at room temperature and decomposes into carbon dioxide and a primary amine. The primary amine is reactive with the polyisocyanate producing a urea and resulting in a turbid formulation or precipitation of crystals of polyurea. The polyisocyanate formulation then becomes generally unusable for forming thermosetting polyurethanes possessing excellent coating properties.
A number of moisture scavengers have been suggested or marketed for moisture scavenging in such polyisocyanate oligomer or prepolymer formulations. Among the many commercially available moisture scavengers are monomeric monoisocyanates such as p-toluene sulfonyl isocyanate, a Zoldine MS Plus product based on oxazalidone, an Incozol 2 based oxazolane, an orthoformate based additive known as OF, and trimethyl orthoformate (TMOF) and trimethyl orthoacetate (TMOC), moisture scavengers. The monomeric isocyanates are generally toxic and considered to be a health hazard. Moreover, on addition to the polyisocyanate oligomer, it causes yellowing when stored over time. The MS Plus product also causes yellowing over time when put into contact with polyisocyanate oligomers or prepolymers. Incozol 2 reacts with water to form an aminoalcohol and 2-ethyl hexanal. The aminoalcohol will react with the polyisocyanate as a chain extender without forming the desired product. The orthoformates and orthoacetates also undesirably readily react with water. The products will form precipitates or cause turbidity in the polyisocyanate solutions.
There is therefore a need for a non-toxic moisture scavenger composition which will effectively and safely isolate water from the polyisocyanates formulations and to do so without causing the aforesaid undesirable occurrences and without adversely effecting the performance and properties of the resulting thermosetting polyurethanes produced from the polyisocyanates.